Online Drought Indicators and Indices

Standardized Anomaly Index (SAI)


Index name: Standardized Anomaly Index (SAI).

Ease of use: Yellow.

Origins: Introduced by E.B. Kraus in the mid-1970s and was examined closely by Katz and Glantz at the National Center for Atmospheric Research, United States, in the early 1980s. SAI was developed based on RAI, and RAI is a component of SAI. They are similar, but both are unique.

Characteristics: Based upon the results of RAI, and was developed to help identify droughts in susceptible regions, such as the West African Sahel and north-east Brazil. RAI accounts for station-based precipitation in a region and standardizes annual amounts. Deviations are then averaged over all stations in the region to obtain a single SAI value.

Input parameters: Precipitation at monthly, seasonal or annual time steps.

Applications: Identifying drought events, especially in areas frequented by drought.

Strengths: Single input, which can be calculated for any defined period.

Weaknesses: Only uses precipitation, and calculations are dependent on quality data.

Resources: Equations for the calculations are provided in the literature.

Katz, R.W. and M.H. Glantz, 1986: Anatomy of a rainfall index. Monthly Weather Review, 114: 764–771. DOI: 10.1175/1520-0493(1986)114<0764:AOARI>2.0.CO;2.

Kraus, E.B., 1977: Subtropical droughts and cross-equatorial energy transports. Monthly Weather Review, 105(8): 1009–1018. DOI: 10.1175/1520-0493(1977)105<1009:SDACEE>2.0.CO;2.

    December 5, 2020 Reply

    How can I calculate the Standardized Anomaly Index

    1. Robert Stefanski
      February 16, 2021 Reply

      Dear Kidist,

      Thank you for your question. Here is the online page for the Standardized Anomaly Index. There are two references with links on this page.

      Best regards,

      IDMP TSU

  2. galgalo
    May 13, 2019 Reply

    so how to calculate or method to calculate

    1. Katrin Ehlert
      May 20, 2019 Reply

      Dear galgalo

      Thank you for your comment. In the references section of the Standardized Anomaly Index (SAI) you can find links to relevant literature defining the index as well as giving application examples.

      Best regards
      IDMP Team

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